Implementation for a simple order-preserving encryption scheme.

This is meant for use when encrypting the current time within the
period in order to get a monotonically increasing revision counter
without actually revealing our view of the time.

This scheme is far from the most state-of-the-art: don't use it for
anything else without careful analysis by somebody much smarter than
I am.

See ticket #25552 for some rationale for this logic.

1 files changed, 40 insertions, 0 deletions

diff --git a/src/test/ope_ref.py b/src/test/ope_ref.py
new file mode 100644
index 0000000000..3677e57a61
--- /dev/null
+++ b/src/test/ope_ref.py
@@ -0,0 +1,40 @@
+#!/usr/bin/python3
+# Copyright 2018, The Tor Project, Inc. See LICENSE for licensing info.
+
+# Reference implementation for our rudimentary OPE code, used to
+# generate test vectors. See crypto_ope.c for more details.
+
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.primitives.ciphers.algorithms import AES
+from cryptography.hazmat.backends import default_backend
+
+from binascii import a2b_hex
+
+#randomly generated and values.
+KEY = a2b_hex(
+    "19e05891d55232c08c2cad91d612fdb9cbd6691949a0742434a76c80bc6992fe")
+PTS = [ 121132, 82283, 72661, 72941, 123122, 12154, 121574, 11391, 65845,
+        86301, 61284, 70505, 30438, 60150, 114800, 109403, 21893, 123569,
+        95617, 48561, 53334, 92746, 7110, 9612, 106958, 46889, 87790, 68878,
+        47917, 121128, 108602, 28217, 69498, 63870, 57542, 122148, 46254,
+        42850, 92661, 57720]
+
+IV = b'\x00' * 16
+
+backend = default_backend()
+
+def words():
+    cipher = Cipher(algorithms.AES(KEY), modes.CTR(IV), backend=backend)
+    e = cipher.encryptor()
+    while True:
+        v = e.update(b'\x00\x00')
+        yield v[0] + 256 * v[1] + 1
+
+def encrypt(n):
+    return sum(w for w, _ in zip(words(), range(n)))
+
+def example(n):
+    return ' {{ {}, UINT64_C({}) }},'.format(n, encrypt(n))
+
+for v in PTS:
+    print(example(v))